This invention relates to catalytic dewaxing and hydrogenation of hydrocarbon feed materials using a catalyst of improved high temperature stability. In a specific aspect, the invention relates to a single step catalytic dewaxing and hydrotreating process for production of lube oil base stocks from a wide range of feeds including relatively low quality, contaminant-containing, waxy hydrocarbon feeds.
Catalytic dewaxing of petroleum and synthetic crude oil fractions in the presence of shape selective catalysts capable of selectively cracking n-paraffins and isoparaffins is well known. For example, U.S. Pat. No. Re. 28,398 (Chen et al.), which is a reissue of U.S. Pat. No. 3,700,585, discloses the use of shape selective crystalline aluminosilicate zeolite ZSM-5 in catalytic dewaxing processes directed at removing high freezing point paraffins from jet fuel to lower the freezing point, improving the octane rating of naphtha fractions and lowering the pour point of lube oil base stocks. According to Chen et al. the shape selective cracking ability of crystalline aluminosilicate ZSM-5 permits selective cracking of n-paraffins and certain isoparaffins without substantial cracking of desirable feed components such that improved catalytic dewaxing products are obtained under both hydrotreating and hydrocracking conditions. Chen et al. also discloses the use of crystalline aluminosilicate zeolite ZSM-5 associated with hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium, such metals being associated with the zeolite by exchange or impregnation.
An abstract of U.S. Pat. No. Re 30,529, which is a reissue of U.S. Pat. No. 4,100,056, discloses catalytic dewaxing of atmospheric and vacuum distillates in the presence of a catalyst containing mordenite in hydrogen form and a Group VI or VIII metal to obtain naphthenic lube oils of intermediate viscosity index and pour points ranging from -50.degree. to +20.degree. F.
An abstract of U.S. Pat. No. 4,222,855 discloses catalytic dewaxing of 450.degree.-1,050.degree. F. hydrocarbon fractions to produce high viscosity index lube oils employing a catalyst containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35, preferably in hydrogen form and associated with platinum, palladium or zinc. According to the abstract, the use of catalysts containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35 gives products of higher viscosity index and lower pour point than products obtained through the use of crystalline aluminosilicate zeolite ZSM-5.
U.S. Pat. No. 4,247,388 (Banta et al.) is directed to improving crystalline aluminosilicate zeolites such as ZSM-5 in terms of dewaxing performance by treatment to adjust alpha activity. According to the patentee, alpha activity is adjusted by partial replacement of cationic sites of the crystalline aluminosilicate zeolite with basic cations such as sodium, by partial coking of the zeolite, by employing the zeolite in combination with an inert matrix material, by manipulating the silica to alumina ratio of the zeolite, or preferably, by steaming. Crystalline aluminosilicate zeolites adjusted in terms of alpha activity can be employed in association with exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium. A disclosure similar to that of Banta et al. is found in an abstract of British Pat. No. 2,027,742.
U.S. Pat. No. 4,251,348 and U.S. Pat. No. 4,282,085 (both O'Rear) are directed to processes similar to those described hereinabove wherein a low nitrogen content petroleum distillate fraction boiling from 180.degree.-1,200.degree. F. is contacted with crystalline aluminosilicate zeolite ZSM-5 or a similar crystalline aluminosilicate zeolite in a form substantially lacking in hydrogenation activity to form an effluent which then is fractionated into an upgraded product stream and a C.sub.3 -C.sub.4 olefin fraction. If desired, the crystalline aluminosilicate zeolite can be dispersed in a porous matrix having only insubstantial cracking activity. Suitable matrix materials include pumice, firebrick, diatomaceous earth, alumina, silica, zirconia, titania, amorphous silica-alumina mixtures, bentonite, kaolin, silica-magnesia, silica-zirconia or silica-titania. A similar disclosure is found in an abstract of Belgium Pat. No. 877,772.
U.S. Pat. No. 4,259,174 (Chen et al.) discloses catalytic dewaxing of hydrocarbon feeds to reduce pour point and produce high viscosity index distillate lube oil stocks in the presence of a synthetic offretite crystalline aluminosilicate zeolite catalyst which may contain exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium. The crystalline aluminosilicate zeolite may be dispersed within a matrix of alumina, silica, silica-alumina, etc. Column 5 line 67-Column 6 line 17. It is unclear whether the patentee contemplates use of the crystalline aluminosilicate zeolite in association with both hydrogenating metals and matrix materials.
An abstract of British Pat. No. 2,055,120 (Mobil) discloses a method for reclaiming or upgrading contaminated, dewaxed lube oil base stocks having a tendency to form a waxy haze during storage, comprising contacting the oil with hydrogen at 500.degree.-675.degree. F. and space velocity of 2-10 in the presence of a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least 12 and a constraint index of 1-12.
In preparation of lube oils from hydrocarbon feeds, catalytic dewaxing processes such as described hereinabove often are combined with hydrotreating, hydrocracking and/or various solvent extraction steps to obtain products having desired properties. Typically, hydrocracking and/or solvent extraction steps are conducted prior to catalytic dewaxing to remove components such as metal-containing feed components, asphaltenes and polycyclic aromatics having properties that differ grossly from those desired. In particular, solvent extraction is conducted to remove polycyclic aromatic feed components and nitrogen-containing cyclic components, removal of the latter being particularly important in order to avoid poisoning of catalyst in catalytic dewaxing. Hydrotreating under mild or severe conditions typically follows catalytic dewaxing operations and serves to improve such lube oil properties as stability and viscosity index.
As one example of a process for producing lube oils in which a catalytic dewaxing step is included as part of a multistep process, U.S. Pat. No. 4,259,170 (Graham et al.) discloses a process that includes a combination of catalytic dewaxing and solvent dewaxing steps. According to a more specific aspect of Graham et al., the process includes a solvent extraction step prior to the dewaxing steps. As a further example of a multistep process for preparation of lube oils, Chen et al. '174, discussed hereinabove, discloses a process comprising solvent extraction followed by catalytic dewaxing. Finally, U.S. Pat. No. 4,283,272 (Garwood et al.) discloses preparation of lube oils by a process that includes hydrocracking, catalytic dewaxing and hydrotreating steps. In each of these multistep processes, the catalytic dewaxing step employs a catalyst containing a crystalline aluminosilicate zeolite, and optionally, exchanged or impregnated hydrogenating metals.
It can be appreciated that multistep processes for preparation of lube oils such as those described hereinabove would be improved if they could be simplified to reduce the number of operations required to attain lube oil base stocks having a desirable combination of properties while retaining applicability with respect to a wide range of feeds. It is an object of this invention to provide an improved process for preparation of lube oils. A further object is to provide a single step process for preparation of lube oil base stocks. Another object of the invention is to provide an improved catalytic process for production of lube oils of low pour point and high viscosity index from a wide range of feeds including even those typically regarded as economically unsuitable for use in multistep processes. A still further object of the invention is to provide an improved process for catalytic dewaxing-hydrotreating of petroleum and synthetic crude oils and fractions thereof. Other objects of the invention will be apparent to persons skilled in the art from the following description and the appended claims.
We have now found that the objects of this invention can be attained by catalytic dewaxing-hydrotreating of hydrocarbon feeds in the presence of an improved catalyst comprising a shape selective zeolitic cracking component and a hydrogenating component of improved thermal stability comprising a chromium component, at least one other Group VIB metal component and at least one Group VIII metal component. Advantageously, catalytic dewaxing-hydrotreating in the presence of such catalytic compositions can be conducted under conditions somewhat more severe than those in conventional catalytic dewaxing processes such that substantial denitrogenation, desulfurization and hydrogenation, as well as selective cracking of waxy feed components takes place. Accordingly, not only are waxy feed components cracked according to the present invention, but also, feed impurities such as sulfur, oxygen and nitrogen are removed. Such results are surprising in view of prior art efforts to reduce levels of contaminants, and particularly nitrogen, by solvent extraction prior to catalytic dewaxing. In fact, according to one aspect of the invention, lube oil stocks of desirably low pour point, high viscosity index and good stability are produced from hydrocarbon feeds which may contain appreciable levels of aromatic feed components and contaminants such as sulfur, nitrogen or oxygen, by a single step process involving catalytic dewaxing-hydrotreating in the presence of the aforesaid catalyst. Suitable feeds according to this aspect of the invention include not only higher quality hydrocarbons of the type commonly employed in processes for preparation of lube oils, but also, low quality hydrocarbons typically regarded unsuitable even for multi-step processes. In addition to the highly desirable results attained in preparation of lube oil stocks according to the present invention, the invented catalytic dewaxing-hydrotreating process yields desirable results in treatment of high sulfur, waxy crude oils such as Great Salt Lake crude oil which is so waxy that it cannot be pumped until wax content has been reduced.
In connection with the present invention, it is to be noted that hydrogen processing catalysts containing a hydrogenating component comprising a chromium component, a molybdenum component and at least one Group VIII metal component are known as are various processes for using the same. For example, U.S. Pat. No. 4,224,144 (Hensley et al.) discloses and claims hydrotreating of petroleum distillates and similar feeds using the aforesaid catalysts to attain improved results in terms of denitrogenation and desulfurization. Further, in our co-pending, commonly assigned application Ser. No. 200,536 filed Oct. 24, 1980, we have disclosed and claimed catalytic compositions containing the aforesaid hydrogenating component, a porous refractory inorganic oxide component and a crystalline molecular sieve zeolite component. Such catalysts are particularly useful in hydrodenitrogenation and hydrocracking of high nitrogen feeds. Suitable zeolites according to such earlier application include shape selective crystalline molecular sieve zeolites among others.